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Plant trichomes have mixed impacts on predatory insects

Eric W. Riddick, Alvin M. Simmons
Pest management science 2014 v.70 no.11 pp. 1668
cages, greenhouse experimentation, greenhouses, insect behavior, photoperiod, plant response, predatory insects, predatory mites, trichomes
In response to our review article on the role of plant trichomes on insect predators (Riddick & Simmons 2014), Krimmel (2014) acknowledged the challenges that are faced in bringing together the varied publications on the subject of impact of plant trichomes on predatory insects. He also suggested that predatory insects may perform better on plant trichomes in the field than one may think, notably because laboratory and field results do not always agree. Certain predatory insects in the field represent a subset of the overall assessment of the impact of plant trichomes on insect predators. We recognize that every publication on this subject was not listed in our review (Riddick & Simmons 2014). On the other hand, we believe that our review summarized the majority of the most relevant published research on this subject. As noted in our review, data for many insect predators are absent or scarce in regards to impact of plant trichomes; our overall conclusions were based on the published data. Moreover, as noted in our review, we excluded predatory mites because they were recently addressed in a review of the impact of plant trichomes on this group (Schmidt 2014). Nevertheless, the published reports in our review show that guilds of insect predators in assorted plant systems can have responses to plant trichomes that range from no effect to mild effect to major effect. Depending on whether research is conducted in a laboratory, greenhouse or field, there are obviously strengths and limitations for each study environment. Sometimes, there are cage effects or environmental effects on plants or insects in studies in either research environment (Simmons & Yeargan 1990; Richards & Coley 2008, Asiimwe et al 2013). For example, plant trichome type and density can vary based on day length (Snyder et al 1998). As illustrated in our review, a host of abiotic and/or biotic factors may even offer different results in the field between two seasons. Yet, data within tri-trophic relationships in different environments (laboratory, greenhouse or field) do not necessarily need to agree to be valid. Of course, the two practical systems for predators in horticultural production systems are protected environments (e.g. greenhouses) and the field. We do not expect plant trichomes to have the same (or lack of) impact on all insect predators in both protected and open field plant systems because of possible differences in insect densities, differences in prey complex, and possible differences in abiotic effects on plants and insect behavior. Although most studies in our review indicated a negative impact on the behavior of predators, the actual impact on fitness is not known. The range of responses lead us to conclude that some predators are apparently more adapted to certain plant trichomes. For some insect predators, the effect is positive, but it is neutral or negative for others. The majority of reports support a negative impact. Yet, much more data are needed to better define which predators are affected by plant trichomes.